1. Field of the Invention
The present invention relates to a collapsible blood reservoir for use in a cardiopulmonary bypass system.
2. Description of the Prior Art
Generally, a cardiopulmonary bypass system is a medical system used in cardiovascular surgery, intensive care and surgical recovery that is coupled to a human body to revitalize and pump blood, thereby performing certain functions of the heart and lungs and often partially or fully bypassing a portion of the circulatory system. The cardiopulmonary bypass system receives a venous blood feed (oxygen deficient blood) from the human circulatory system, oxygenates and typically transfers heat with the blood and returns the blood to the circulatory system at a flow rate approximately corresponding to the venous drainage, thus reducing the load on the lungs and heart.
A cardiopulmonary bypass system in a partial support capacity is used, for example, during cardiac intensive care of patients who have suffered a cardiac infarction where a portion of the heart muscle has died from an insufficient blood supply. The dead muscle is soft and difficult to suture since it will tear easily. The muscle may heal if the patient is kept quiet and heart chambers are subject to a minimum amount of pressure. Failing such care, an aneurysm may result in which the softened muscle swells up and stagnates pools of blood which tend to clot. The tendency toward development of an aneurysm is minimized reducing the pumping load on the heart with the partial support system. Typically the infarcted tissue scars over and thereby regains its tensile integrity in several weeks during which time the cardiopulmonary bypass system must operate continuously. Recent developments in pump oxygenation equipment, such as membrane oxygenators having limited long term blood degradation effects, have made possible long term partial support of this duration.
Many specific requirements must be met in a practical partial support system. For example, the cardiopulmonary bypass system experiences a load as the blood is returned to the human body. The load is variable and the flow impedance seen by the cardiopulmonary bypass system may increase if, for example, the arteries are constricting or decrease when hemorrhaging is occurring. Yet the cardiopulmonary bypass system should generally maintain a constant flow rate to the human body, equal to the venous drainage.
The rate and changes in rate of blood flow indicates the physical state of the patient, and thus it would be desirable to monitor the blood flow rate. The physician may find it necessary to increase or decrease the return flow rate of the blood. Increasing the blood flow rate in excess of the drainage rate often requires the addition of blood to the system. It would be advantageous to have a cardiopulmonary bypass system which could introduce quantities of blood to the blood flow in addition to the blood supplied by the patient's circulatory system.
The quantity of blood flowing in the circulatory system of a young infant is extremely critical. For example, hyaline membrane disease attacks the alveolar sacks of infants. When this occurs, the lining of the lungs is impervious to oxygen and CO.sub.2. Since the infant having this disease receives insufficient oxygen, the treatment in the past has been to increase, in concentration and pressure, the oxygen provided to the infant. Although the disease is often cured by this technique, other serious conditions may set in which are caused by the toxic effects of oxygen such as retrolental fibroplasia, in which the retina is destroyed. By using a cardiopulmonary bypass system, the lungs are allowed to heal. The control of blood volume is extremely important since the hyaline disease typically occurs with underweight infants, typically less than 2500 grams and having a total blood volume of only 150-300 cc.
Thus, it would be desirable to have a cardiopulmonary bypass system that is safe, reliable and volume alterable.